diff --git a/src/chunk.c b/src/chunk.c
index 56070e28a..7e90ee6e2 100644
--- a/src/chunk.c
+++ b/src/chunk.c
@@ -149,10 +149,9 @@ int chunk_printf(struct buffer *chk, const char *fmt, ...)
 	va_start(argp, fmt);
 	ret = vsnprintf(chk->area, chk->size, fmt, argp);
 	va_end(argp);
-	chk->data = ret;
 
 	if (ret >= chk->size)
-		ret = -1;
+		return -1;
 
 	chk->data = ret;
 	return chk->data;
diff --git a/src/proto_http.c b/src/proto_http.c
index 999c39ebf..6a1722f39 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -3845,8 +3845,7 @@ int http_process_request(struct stream *s, struct channel *req, int an_bit)
 	}
 
 	if (sess->fe->header_unique_id && s->unique_id) {
-		chunk_printf(&trash, "%s: %s", sess->fe->header_unique_id, s->unique_id);
-		if (trash.data < 0)
+		if (chunk_printf(&trash, "%s: %s", sess->fe->header_unique_id, s->unique_id) < 0)
 			goto return_bad_req;
 		if (unlikely(http_header_add_tail2(&txn->req, &txn->hdr_idx, trash.area, trash.data) < 0))
 		   goto return_bad_req;